I've been reading a lot about cortisol recently, and it seems that the complexities of this hormone in terms of what effects it, and in turn what it effects, have been drastically oversimplified in the Paleo community. Like many other substances and states -- cholesterol, inflammation, antioxidants, even insulin -- the optimal state is not to have none, but to have an appropriate amount at the appropriate time.

In particular, the idea that lowering cortisol is always a healthful strategy, is as misguided as indiscriminately aspiring to lower cholesterol.

Can anyone cite situations in which high cortisol is desirable, list useful things it does in the body, or provide any other relevant knowledge about cortisol levels?

Here are just a few possibly counter-intuitive facts about cortisol I've come across that I think merit more weight.

(1) Cortisol has differential effects depending on insulin state. In the paper Regulation of Lipogenesis by Glucocorticoids and Insulin in Human Adipose Tissue, which I am only just beginning to digest and understand, the authors state:

In the fasting state, low insulin levels and high endogenous GC levels will stimulate lipolysis and simultaneously switch off lipogenesis though serine phosphorylation of ACC1, decreasing fuel storage and increasing FFA availability for other more metabolically active tissues. Conversely, in the fed state, insulin levels are high, and here insulin and GC may act together to promote lipid storage.

So it seems plausible that if you were trying to lose fat, and you had already taken measures to lower your insulin levels, then higher cortisol would be beneficial. Whereas if your insulin levels are high, more cortisol would only increase your fatness.

(2) High cortisol raises leptin, that elusive, misunderstood and longed-for hormone.

I'm not going to discuss this point further, because leptin is another very complex topic that I think is not well understood by almost anyone. It's just a point for consideration.

(3) Cortisol is anti-inflammatory. Given this fact, it makes sense that long-term high levels of cortisol could be indicative of, and a response to, chronic inflammation, thus the association of high cortisol with disease states. On the other hand, there is a certain sense in which we want regular anti-inflammatory action in the body, just as we want anti-oxidant action. So if cortisol rises after intense exercise, for example, that is probably desirable.

This situation is comparable to what we want from insulin. Even the most staunch low-carber needs an appropriate insulin response after eating. What they don't want is any excess insulin, or especially chronically elevated insulin.

(4) Levels of cortisol are dependent not just on adrenal production, but on regeneration outside the adrenals and urinary loss of cortisol metabolites. Thus, your levels of cortisol are not necessarily indicative of how hard your adrenals are working! As we know from adrenal fatigue, lowering levels of cortisol can actually be indicative of adrenal stress, and the inability to keep up with demand.

That last bit is crucial to understand if you are concerned about stressing your adrenals. An important strategy to consider for relieving adrenal stress is making sure that the cortisol your adrenals do make is used as long as possible. That means it is regenerated outside of the adrenal glands, and that the metabolites aren't lost in the urine.

This study, Dietary Macronutrient Content Alters Cortisol Metabolism Independently of Body Weight Changes in Obese Men suggests that a ketogenic diet has this cortisol-sparing effect, independent of weight loss.

In obese men, an HF-LC diet increased whole-body regeneration of cortisol by 11β-HSD1 and reduced the rate of inactivation of cortisol by 5α- and 5β-reductases.

Glycyrrhizic acid, found in licorice, also has this effect, and that's why it is often recommended for adrenal support.

In short, if something raises (or for that matter, lowers) your cortisol levels, the desirability of that effect is not necessarily easy to interpret. It could be causing fat loss or fat gain depending on environment. It could be an appropriate, temporary, anti-inflammatory response to something essentially healthful, like exercise, or it could be an indicator of chronic inflammation. It could indicate overproduction and therefore an adrenal stress, or it could indicate better regeneration and less clearance: a relief of adrenal stress. Like just about everything else we encounter, cortisol is not a universal villain.